Two-electron transfer photoreduction of methyl viologen and perfluorooctanoic acid mediated by flavin mononucleotide at colloidal titanium dioxide interfaces

Flavin mononucleotide (FMN) in methanol was photochemically reduced to FMNH2, which undergoes electron transfer with Methyl viologen (MV2+) in ethanol. This charge transfer interaction results in the reduction of MV2+ into MV+˙, as well as the storage of electrons. The spectroscopic experiments allow for the elucidation of quantitative electron transfer into MV2+. To study the redox potential for FMN species, the HOMO and LUMO energies were calculated using density functional theory (DFT) method on the B3LYP level with a basis set of 6-311G(d,p). The HOMO and LUMO energy calculations show that the redox state of FMNH2 is energetically more favorable than FMNH˙ for MV2+ reduction. These studies revealed good agreement between the experimental results and computational predictions. Moreover, molecular electrostatic potential (MEP) was performed on the FMNH2-MV2+ complex to determine the site of electron transfer, and the results were compared to the experimental results. FMN functionalized to the surface of colloidal titanium dioxide nanoparticles (TiO2 NPs) showed enhanced reactivity toward the reduction of perfluorooctanoic acid (PFOA). The two-electron transfer reduction process is generated by irradiating FMN attached to TiO2, during which FMN reduces to FMNH2. The FMNH2 then reacts with PFOA to produce shorter chain structures with fewer fluorine atoms, such as C5F11COOH. The results indicate that the rational organization of FMNH2/TiO2 to mediate two-electron transfer is effective for the reductive degradation and remediation of PFOA.